Spanish use of chemical weapons in the Rif War

During the Third Rif War in Spanish Morocco between 1921 and 1927, the Spanish Army of Africa deployed chemical weapons in an attempt to put down the Berber rebellion against colonial rule in the region of Rif led by the guerrilla Abd el-Krim.^[1] Following the humiliation at the Battle of Annual in 1921, considered as the worst Spanish defeat in the 20th-century, the Spanish army pursued a vicious campaign of retribution involving the indiscriminate and routine dropping of toxic gas bombs targeting civilian populations, markets and rivers.^[2]

These attacks in 1924 marked the first widespread employment of chemical warfare in the post-WWI era^[2] and the second confirmed case of mustard gas being dropped from airplanes. While Spain signed the Geneva Protocol a year later, which prohibited the use of chemical and biological weapons, such use was not illegal in non-international armed conflicts.^[3][4][2]

While Spain pursued its chemical campaign in secrecy from the public, French intelligence provided Spain with weapon systems including tear gas and smaller gas agents, and a German company helped Spain obtain more effective chemical agents.^[2] The gas used in these attacks was produced by the "Fábrica Nacional de Productos Químicos" (National factory of chemical products) at La Marañosa near Madrid; a plant founded with significant assistance from Hugo Stoltzenberg, a chemist associated with clandestine chemical warfare activities in the early 1920s^[5] who was later given Spanish citizenship.^[6]